1. Field of the Invention
The present invention relates to a method of making an antibacterial material and more particularly, to a one-pot process of synthesizing nano-scaled silver-containing waterborne polyurethane (hereinafter referred to “WBPU”). The method of the present invention can be easily and rapidly operated, and a film formed by a polyurethane emulsion prepared according to the method of the present invention contains uniform-sized and well-dispersed nanoparticles.
2. Description of the Related Art
Because of the progress of nanotechnology in the past years, making nano-scaled inorganic oxide or metallic particle has become possible. Since the increase in surface area to volume ratio makes the nano-scaled particles exhibit physical and chemical behaviors different from those of the conventional particles. The nano-scaled particles also have excellent quantum effects.
A small amount of metallic silver or silver ion is sufficient to kill bacteria by destroying the bacterial protein, such that metallic silver and silver ion have been applied to antibacterial, bactericidal, and deodorant against, especially E. coli, staphylococcus aureus, mold etc., all the time.
By means of the excellent film coating and forming property of polymer, polymer emulsion prepared by blending nano-scaled inorganic metal or metal oxide with polymer can be coated onto a variety substrates to form thin films. The resulting film exhibits antibacterial property even though a small amount of nano-scaled inorganic metal or metal oxide is used, thereby having economic benefit. However, inorganic metal or metal oxide can be hardly uniformly dispersed in organic polymer emulsion. Specially, the nano-scaled particles tend to flocculate together. Thus, the nano-scaled particles can not be uniformly dispersed in the resultant film formed by the polymer emulsion, resulting in color difference and mechanical property deterioration thereof.
To resolve the above-mentioned problems, several approaches have been typically used as follows: (1) surface-modifying the nano-scaled particles, so that the particles can be dispersed in the organic polymer easily; (2) mixing the nano-scaled particles with dispersing agent in advance, and then blending the mixture thus obtained with polymer, in which the dispersing agent is used as a medium; and (3) blending the nano-scaled particles with a polymer having the property of a dispersing agent, so that the nano-scaled particles can be dispersed uniformly in the polymer by utilizing the polymer chain to separate the nano-scaled particles.
However, the aforesaid approaches have many drawbacks. For example, because the nano-scaled silver particles have to be synthesized first, and then modified and dispersed in the polymer, the manufacturing process becomes complicated and time-consuming. Second, because a modifier or a dispersing agent is adsorbed on the surface of the blended nano-scaled silver particles, the properties of the blended nano-scaled silver particles are less effective and the mechanical and thermal properties of the blended polymer may be also affected. Thirdly, because a modifier is adsorbed on the surface of the surface-modified nano-scaled silver particles, the effective weight of the surface-modified nano-scaled silver particles cannot be easily measured. Fourthly, the modified nano-scaled silver ion particles or nano-scaled silver particles with dispersing agent still can not be completely uniformly dispersed. Fifthly, the sizes of commercially available nano-scaled silver particles are uneven in size at present.
FIG. 1 shows a transmission electron microscopy image of commercial available nano-scaled silver particles. It can be seen from FIG. 1 that the sizes of the nano-scaled silver particles are uneven, in which the maximum particle size is about 50 nm and the minimum particle size is about 10 nm. FIG. 2 shows a transmission electron microscopy image of silver-containing WBPU obtained by mixing the commercially available nano-scaled silver particles with the WBPU emulsion thoroughly. As shown in FIG. 2, the nano-scaled silver particles are not uniformly dispersed in the silver-containing WBPU.